The present invention relates to measuring or sensing arrangements in general, and more particularly to an arrangement for continuously determining the cross section or mass of an elongated strip-shaped web of fiber sliver.
There are already known various arrangements of the above type, among them such in which the web passes through a nip between two sensing rollers, one of which is mounted for rotation about a stationary axis and is driven in rotation, while the other is mounted for free rotation about another axis which is parallel to the stationary axis and defines an imaginary plane therewith, and for movement along the imaginary plane against a spring force away from the one roller, and in which sensing means senses the extent of movement of the other roller relative to the one roller.
So, for instance, the published German patent application DE-AS No. 12 65 631 discloses a drafting arrangement in which fiber sliver is guided between a driven roller rotating about a stationary axis and an additional roller which can be pressed against the driven roller and is frictionally entrained for rotation about another axis. A pulse generator, which is not described in any detail in this published application, engages the additional roller and generates a signal in dependence on the movement of this additional roller, this signal being supplied to control means which is operative for correspondingly varying the rotational speed of the driven roller.
This particular known arrangement has several disadvantages, one of which is that the engagement of the pulse generator with the additional roller causes friction which results in wear of the sensing surface of the pulse generator. Another drawback of this known arrangement is that error measurements may result if foreign particles or bodies pass between the sensing surface of the pulse generator and the associated surface of the additional roller. This is particularly true if the foreign particles or bodies are of a smearable, layer-forming type. Such error measurements can remain undetected over a long period of time, thus producing undesirable faults in the yarn count over a considerable length of the produced yarn.